The theoretical framework for investigating human planning behavior and the procedures, results, and implications of two experiments involving planning in the domain of software design are presented in this report. A plan is defined as a hierarchical structure that underlies the solution to a problem; planning is the process of constructing this structure. This framework makes various assumptions about the nature of a plan and the construction of the planning structure. Experiment one involved the collection of long, thinking-out-loud protocols from three highly experienced computer scientists. Experiment two involved ten undergraduate college students enrolled in an "assembly language" course who were instructed to solve a design problem similar to the one given to the experts in either a written-solutions condition or a written-and-think-aloud condition. Examination of the experimental behaviors indicate that completed plans can be characterized in a variety of ways. Expert subjects differ from less experienced subjects in the knowledge structures that can be retrieved from long-term memory and incorporated into a plan. (Author/CWM)